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Herbicide-Resistant Sunflowers Have Roots in ARS Research

By Jan Suszkiw
January 3, 2005

HA 245 and RHA 426 sound like the names of super-secret spy planes. The truth is more mundane, though no less important to sunflower growers: HA 245 and RHA 426 are strains of sunflower germplasm that have given rise to the oilseed crop's first herbicide-resistant cultivars.

Agricultural Research Service geneticist Jerry Miller developed the germplasm by crossing cultivated sunflower with the weedy relative Helianthus annuus. He began the crosses in 1998 after learning of weed physiologist Kassim Al-Khatib's research findings. In studies at Kansas State University, Al-Khatib showed that some H. annuus specimens could withstand being sprayed with the postemergence herbicide imazamox.

That observation generated considerable excitement; transferring such resistance into cultivated sunflower could enable growers to spray weed-infested fields without killing their crop in the process, according to Miller, at the ARS Red River Valley Agricultural Research Center in Fargo, ND.

Miller germinated the seeds of 300 H. annuus specimens from Al-Khatib's collection, and then sprayed the young plants with herbicide to identify the hardiest survivors. From 28 candidates, he chose six to cross with cultivated sunflowers, producing five generations of crossbred progeny in one year. Backcrossing eliminated unwanted traits like multiple flower heads. Each time, Miller used embryo rescue, a technique for side-stepping fertilized seed's lengthy dormancy stage.

In 2002, Miller and colleagues' hard work paid off with the public release of HA 245 and RHA 426 as breeding stock that commercial seed companies could use to produce farmer-ready cultivars. Those cultivars, known as Clearfield sunflowers, debuted in 2003, with further releases made in 2004.

Clearfield sunflowers' herbicide resistance should be especially useful in drought-prone regions where fields are left unplowed, a conservation practice that can give dominant weed species a chance to sprout and cause problems later on, according to Miller.

Read more about the research in the January 2005 issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief scientific research agency.